Free radicals are intermediates in every one-electron oxidation or reduction of an iron porphyrin or hemeprotein by an organic molecule. Indeed, we have demonstrated their intermediacy in the oxidation of hemes and hemeproteins by alkyl halides, nitroaromatics, quinones, and oxygen. They are also intermediates in the reduction of the corresponding iron(III) complexes by hydroquinone and in the "reductive conversion" of oxyhemoglobin to methemoglobin. Organic radicals are intermediates in every redox process we have examined with iron porphyrins. Moreover, some of the radicals are likely to be directly involved in mitochondrial electron transport (semi-quinones) or in the biological reduction (hydrogen atoms) or oxidation (hydroxy radicals) of hemeproteins. The rates of the generation and destruction (by cytochrome P450?) of these highly reactive fragments could be an important balance to maintaining cellular integrity. The specific objective of this proposal is to discern the nature and mechanism of the oxidation and reduction of iron porphyrins and hemeproteins by certain organic and inorganic free radicals and the molecules from which they emanate. Our long range objective is to explain the biological redox processes of hemeproteins on a firm molecular level.